How To Be ESD Savvy   ESD Safe Packaging There is considerable misconception about what constitues correct ESD safe packaging for assemblies and components.  Let's review the relavent points. Electrostatic Protected Area (E.P.A.) Voltages over 100V are not permitted in a true Electrostatic Protected Area (E.P.A.). All surfaces must be grounded. All personnel must be grounded. No static-generating materials may be present and proper ionization must be incorporated to neutralize residual static. In an ideal E.P.A., only antistatic materials are needed without the requirment for protective packaging to shield the components from static. Electrostatic Protected Area (E.N.P.A.) The area outside the E.P.A. is known as the Electrostatic Non Protected Area (E.N.P.A). It is impossible to control static in an E.N.P.A. environment; therefore, protective shielding packaging is absolutely required to shield components from static sources. Direct Intimate Contact Materials which come in direct contact with components should be antistatic (low tribocharge). This means that rubbing components with packaging materials commonly found inside bags and tubes or foam lining inside boxes will not create a static charge. Proximity Shielding is ALWAYS required whenever components and assemblies are moved out of the E.P.A. in order to minimize danger from uncontrolled electrostatic fields. Commonly available shielded containers are black conductive boxes or metallized surfaces typically found inside shielding bags. Secondary Protective Layer Secondary packaging is the outer layer which covers the shielding layer or the antistatic layer of a bag or of a box. An outer covering is necessary for mechanical protection on corrugated carton boxes, adhesive tape, cellophane, etc. However, all materials without a secondary protective layer covering the outer shielding layer should not be permitted into the E.P.A. because, static charges accumulate on unprotective surfaces and may discharge through components. Faraday Cage The Faraday Cage effect is present whenever a highly conductive "closed" container completely surrounds a sensitive component. When any static field induces a charge on the surface of the packaging, or when any packaging surface comes in contact with another charged surface, a static charge will be induced. Whenever a static charge meets the highly conductive surface of a Faraday Cage, the static will be equally and instantaneously diffused, surrounding the component with the same potential (voltage). In an ideal Faraday Cage, static will NOT enter the packaging because there is no electric potential differential. In other words, a shielding bag or a conductive box will behave as an "insulated conductor" capable of discharging upon first contact with a groundable point, such as an operator's hand or a grounded surface, etc. The Perfect World Here are some useful hints when selecting ESD safe packaging for a component or an assembly: Keep components in direct contact with antistatic, non tribocharging, highly electrically resistent materials. In otherwords store components in antistatic bags or in antistatic foam. Do not allow conductive materials to come in direct intimate contact with components or assemblies because of the following reasons:     1. Conductive materials will cause static to discharge too fast and create possible short-circuiting of the components (sparking danger).     2. Conductive materials will not isolate the contents of the packaging from their own charge. For example, if a person is charged and they touch a conductive bag, the charge is immediately transferred to the contents.     3. Conductive materials are normally carbon loaded; therefore, they may release unwanted higly conductive particles on the assemblies. Components should be isolated. Use highly conductive material for the inner packaging in order to create a Faraday Cage surrounding the components. Remember: for proper use, shielding packaging must completely enclose the contents. In otherwords, do not leave black conductive boxes and shielding bags open. Components which are stored in open packaging in grounded trays or racks will not be protected from outer static fields. Therefore, do not move components in open packaging outside the E.P.A. without first inserting them into conductive boxes or shielding bags. Antistatic (i.e. pink poly) packaging do not offer any shielding for the component; therefore, they should not be relied upon as the only ESD protection outside the E.P.A. Thickness of the Packaging Proper shielding also depends on the thickness of the packaging. For example, a conductive box, lined with antistatic foam, provides better protection than a thin conductive shielding bag. Keep in mind that the contents inside a shielding bag is separated only by a thin layer of antistatic polyethilene. Black conductive boxes on the other hand, provide far more protection between the external charge and the inside world. Additional Remarks Always remember to put ESD warning signs at the boundaries of the E.P.A. so that everyone will know exactly where the control of static protective procedures begins. It is very important to know that inside a package there are contents which are sensitive to static discharge. The outer layer of the ESD package should always be antistatic so that it will not create sparks. By understanding and practicing all of the forgoing points you will protect ESD sensitive components and assemblies. TopLine Corporation 95 Highway 22 W Milledgeville, GA 31061, USA Toll Free USA/Canada (800) 776-9888 International: 1-478-451-5000  •  Fax: 1-478-451-3000 Email: Info Home